Alloys



Patented Feb. 15, 1938 PATENT OFFICE 2,103,050 armors Birger Egeberg, Meriden, Conn.,- and Roy W.

Tindula, Buflalo, N. Y., assignors to International Silver Company, Meriden, Oonm, a corporation of New Jersey No Drawing. Original applicationv December 24, a

1934, Serial No. 759,053.

Divided and this-application April go, 1937, Serial No. 131,915- Claims. (01. 75-111) This invention relates to alloys and this application is a division of application Serial No. 759,053 filed December 24, 1934.

The object of the invention generally is a tar- 5 nish and corrosion resistant alloy which may be readily cold worked, may be melted and cast more easily than prior non-tarnish and non-corrosive alloys, and may be economically produced, and particularly an alloy adapted for use in the manl0 ufacture of tableware and various kinds of hardware where a complete or substantially complete resistance to weak organic acids, salt solutions, and organic sulphur compounds is necessary, or where superior resistance to many strong mineral acids, suchas sulphuric and nitric, is desired.

A further object of the invention is an alloy which, being resistant to tarnish and corrosion by all ordinary materials found in foodstufis, such as sulphur compounds, salt solutions, and weak goorganic acids, requires no super-imposed nontarnish coating for use in the manufacture of tableware, and which is characterized generally by its favorable chemical resistance, desirable physical properties, ease of cold working, ease of *polishing to a high luster, ease of treatment, low melting point, ease of production, and low cost.

To these ends we have produced an alloy embodying chromium, nickel, copper and zinc, all in substantially complete solid solution, and in proportions, coupled with special heat treatment when desired, to endow the same with the desired characteristics above indicated.

The individual elements of the alloy may vary over a limited and prescribed range in percentage but the amounts of nickel and chromium must be carefully controlled and proportioned andthe copper and zinc contents carefully proportioned and balanced against the nickel and chromium contents, with carbon and other impurities kept below predetermined values.

.In order to produce the alloy of our invention which ofiers substantially complete resistance to tarnish and corrosion by household reagents,

foodstuifs, weak organic acids, sulphur compounds, saline or industrial atmospheres, and corrosive vapors, we flnd it necessary that about one atom (or over) of every eight atoms in the alloy be of chromium (that is at least approximately 11 per cent by weight of chromium in solid solution) and furthermore that the other :elementsbe so proportioned that the annealing treatment given will bring this amount of chromium into solid solution. Eor resistancegto the more corrosive materials, such as nitric acid we have found a higher percentage oi chromium than that which corresponds to the .125 atomic fraction (about 11% by weight) to be of great value, as for example up to 20%. In alloys for -use in' applications not involving acid corrosion,

smaller proportions of chromium in solid solution may be employed, as for example as low as four or five per cent.

The nickel content serves to bring the other constituents of the alloy into uniform solid solution and preferably suflicient nickel must be incorporated for this purpose. It also substantially, along with chromium, favorably affects the degree of resistance to various tarnishing and corroding media by effecting the solubility of chromium at various temperatures, and tends to improve the workability and give somewhat increased luster in the polished state, but these advantages are somewhat oifset by increase in melting point, greater cost, darker color, etc. Accordingly, the nickel content is kept as low as 'is permissible, though it may vary from forty to seventy per cent by weight.

By incorporating zinc not only may the proportion of copper and nickel be thereby reduced, but the alloy becomes endowed with certain of the special properties and characteristics above described. For example, while the melting point of pure nickel may be progressively lowered about 50". F. for each 10% of copper alloyed with it, 10% of zinc will lower the melting point by approximately 125 F. Thus with a-given chromium and nickel content the substitution of 10% zinc in place of 10% of copper produces an alloy with a melting point F. lower. This greatly facilitates melting and makes it possible to obtain much more fluid and better ingots. The substitution of 5% to 10% zinc also results in an alloy with greater softness on annealing the cold worked alloy, a better surface on alloys which have been annealed and pickled. greater ease of pickling because annealing furnace scale is more soluble in strong acids, and appreciablybetter resistance for a given chromium and nickel content to tarnish and corrosion in sulphur hearing compounds, salts or weak acids.

While large proportions of zinc tend to reduce the possible rolling reductions between annealings, this eflect is quite small up to proportions of 10% and our alloy with a component of asmuch as 20% or over of zinc still possesses a limited degree. of cold workability. For best results we prefer to use with an alloy containing about 11%. chromium and 50-55% by weight of nickel around 10% zinc, and for alloys of the lower chromium range the zinc content may run up to 20% with advantage. In certain cases larger proportions of zinc may be incorporated,

The copper element, like zinc, aids in obtaining a low melting point and other desired characteristics of the alloy, such for example as its cold working properties, and we have found that by alloying manganese and zinc with copper (and the other elements) and for alloys of the higher chromium range limiting the copper to less than about 30%, with the corresponding proportions of nickel, chromium and ironabove described, superior or complete-resistance of the alloy to tarnish and corrosion by sulphur compounds and organic acids is secured. The presence of copper also aids in the alloying of the zinc with the other elements. The copper content should not be less than 5% of the composition by weight and preferably is substantially larger (around 15%), 5% to 20% for alloys of the higher chromium range, and in alloys of the lower chromium range copper may be alloyed up to a limit of about by weight.

While carbon cannot be entirely eliminated it must be kept below the upper limits described below because it may remove a considerable amount of chromium from effective service in preventing tarnish, thus making a greater chm-- mium content necessary than if it were not present. It tends to form a hard and insoluble constituent within the alloy that greatly impairs malleability and ductibility which can only be partly counteracted by higher nickel contents, and these insoluble particles add greatly to the difiiculty in polishing and if more than the below amounts of carbon are present it is detrimental to the luster of the polished alloy. Maintaining the carbon content as low as possible is of utmost importance in developing the desired properties; also because the carbon content, even in proportions less than the below mentioned amounts, increase the frictional wear resistance of the alloy and is consequently detrimental from the standpoint of. ease of polishing and the amount of labor involved. We have found that the carbon content should not exceed .05 per cent at 35% nickel, .12 percent at 50% nickel, .15 per cent at nickel or .20 per cent at nickel.

The following are examples of embodiments of our invention:

Gammon; ANALYSIS Group I Ni Cr Cu Mn Zn Fe 81 O 00.5 a 7 11 0.3 0.2 00. 0 12. 5 18.0 0. 25 s 5 0. 5 0. 15 0.10 51. 5 15. 0 1a 05 0. 4 1a-7 0. 5 0 1 0.15

Group II 52.5 11.0 zao 10.0 0.3 (12 015 53.0 12.0 20.0 0.4 14.0 0.4 0.1 0.1 55.0 11.5 2&5 0.2 0.3 0.3 0.1 0.1

Group III 41.0 so 42.5 a4 10.0 0.2 0.1 0020 35.9 5.0 3&2 0.1 18.4 0.4 0.1 0.015 48.6 7.2 33.1 0.1 1114 0.5 011 54.3 0.9 18.4 0.3 10.0 0.0 011 0.020

These examples of the alloy show a range in proportions of chromium from around 4 to 15 per cent (may reach 20%), nickel 36 to 70 per cent, zinc from 6 to 18 per cent, and the balance copper in excess of 5 per cent with the carbon content limited as described above.

Group I of the examples includes alloys whose condition of complete immunity to tarnish or corrosion by mayonnaise and vinegar or any other ordinary household agent is obtained by any annealing treatment of commercial duration. These alloys may also be used in the cast condition, after any commercial furnace annealing treatment or after soldering, etc., with substantially complete immunity to tarnish or corrosion. The only exception to this applies to severely stressed or cold worked alloys of this class and also toprolonged heating at temperatures somewhat below 1600 F.

Group II includes alloys which by means of high temperature final annealing treatment (generally from 1900 F. up followed by rapid cooling) 1 can be rendered completely immune to tarnish or corrosion by mayonnaise and vinegar. After final annealings carried out at lower temperatures, alloys in this class are very slightly attacked by these materials. For complete resistance to milder conditions as atmospheric tarnish, corrosion by salt spray, or tarnish by egg or hydrogen sulphide, this high annealing temperature will not be necessary.

Group III includes alloys which are not completely immune to attack by mayonnaise and vinegar but may be somewhat improved in this respect by heat treatment similar to the heat treatment for Group 11. However, any such attack that does take place is much slower and not as severe as would take place on any relatively inexpensive alloys now known to the art which do not contain chromium. At the same time, these alloys in Group III are substantially immune to atmospheric tarnish, corrosion by salt spray, or tarnish by egg or hydrogen sulphide.

In the practical production of the alloy it is impossible to avoid traces of one or more other elements being present as impurities in the essential elements making up the charge or extracted from the furnace lining or slag, such for example as traces of silicon, carbon, cobalt, tin, aluminum, etc., but it is understood that such impurities as described above with respect to carbon are reduced to the lowest practicable value.

Small additions of magnesium to the alloy are harmless, and preferably 0.1 per cent of magnesium as a copper alloy is added to the melt just before pouring to remove oxygen and other harmful gases. For example, in order to produce a sound ingot free of excessive blowholes, it is desirable to add to the melt a small amount of magnesium, aluminum, calcium, barium, lithium, or other strongly reactive metal or alloy. The

preferred practice is to add about one-half pound of a copper alloy containing 20% magnesium to every pounds of total melt one or two minutes before casting.

Any suitable method may be utilized for bringing the constituents of the alloy of our invention into a melt of the desired proportions and the following is merely suggestive of one procedure. It is desirable to use a furnace or crucible lined with a material free or nearly free of carbon. It is very important that the metal come only incontact with non-carbonaceous materials during the melting period.

Chromium may be added in the form of low melting point addition alloys such as a 50-50 chrome-nickel alloy, or a 38-37--25 chromiumnickel-copper alloy. The method of adding the various ingredients to the melt of our invention may be varied in any way provided the ingot analyses produced be within the limits described above.

After the ingot casting is obtained it may be converted into strip, sheet, or any type of hollowware, flatware, hardware or ornamental articles in essentially a similar manner to that now used by the art, viz: hot working, cold working and annealing. Cold rolling and annealing schedules will vary considerably for the'various alloys, but in general it can be stated that most of the alloys embodied in our invention will withstand at least 50% reduction in thickness by cold rolling between successive annealings, and can be made sufiiciently soft for further working by annealing between 1600 and 2000 F.

We have thus set forth the relative proportions of our alloy and have given certain limited ranges in proportions together with certain specific examples and it is understood that the proportions may be varied within the limited range described depending on the particular use to which the alloy is to be put. Where an alloy of maximum workability, luster, and complete tarnish and corrosion resistance is desired, the higher chromium and nickel ranges are to be used. For any material which is to be soldered,

brazed or Welded into finished articles an alloy of our invention containing more than 54% nickel and 11% chromium by weight should be used.

An alloy within the Group I of our invention is suitable asindicated, for use in the cast condi tion for tarnish and corrosion resistance, and, since mechanical workability is not a factor h 'e, we may add about1% of silicon to the alloy ror improved sharpness in casting.

For manufacture of cutlery articles and other materials which require complete or essentially complete non-corrosive and non-tarnish properties, and where the material can be annealed at a high temperature just before or after final fabricating processes either of the embodiments Groups I or II can be used. For example, for

manufacture into spoons, forks, knives, and

other tableware an alloy of our invention containing more than 48% nickel, more than 11% chromium and no greater than 30% copper is preferable. The final annealing treatment before or after fabrication into final form should consist of heating the alloy to a temperature between about 1900 and 2100 F. and cooling rapidly.

For manufacture of hardware and other articles where extreme corrosion resistance is not as important as strength, lower cost, and ease of manufacture, any of the alloys within the limits of our invention set forth previously may be used, with the low chromium alloys of Group III preferred.

We claim:

1. An alloy containing nickel, chromium, zinc and copperin the approximate proportions of 4 to 20% chromium, 36 to nickel, 2 to 18% zinc, and the balance copper, not less than 5%,

with traces of other elementsincluding a small trace of carbon.

2. A cold workable, low melting point alloy having non-tarnish characteristics and consisting of 10 to 20% chromium, 45 to 70% nickel, 2 to 20% zinc and the balance copper, in excess of 5%, with traces of other elements including a small trace of carbon.

3. A .cold workable, low melting point. alloy having non-tarnish characteristics, consisting of chromium, nickel, copper, and zinc, wherein the chromium content is 10 to 20%, nickel 45 to 70%, zinc 2 to 20%, and the balance copper in excess of 5% and not greater than 30%, with traces of other elements including a small trace of carbon.

4. A cold workable, low melting point alloy having non-tarnish.characteristics, consisting of nickel, chromium, copper-and zinc, wherein the chromium content is 4 to 10%, nickel 36 to 60%, zinc 2 to 20%, and the balance copper in excess of 13% and not greater than 55%, with traces of other elements including carbon with the carbon not in excess of 0.2%.

5. A cold workable, low melting point alloy having non-tarnish characteristics consisting of 54 to 70% nickel, 11 to 20% chromium, 5.8 to 25% copper and 1.5120 20% zinc, with traces of other elements including carbon with the carbon not in excess of 0.2%. I

6. A cold workable, low melting point alloy having non-tarnish characteristics and capable of being endowed with increased, corrosion resistance by heat treatment at temperatures between 1900 F. and the melting point consisting of 11 to 15% chromium, 48 to 54% nickel, 5.8 to 30% copper and the remainder zincbetween 6 to 20% and traces of other elements including carbon with the carbon not in excess of 0.2%.

7.;A cold workable, non-tarnish, low melting point alloy which consists of chromium, nickel,

8. An alloy of chromium, nickel, copper andzinc in the proportions of around 11% chromium,

5055% nickel, 5 to 15% zinc and the remainder copper'with traces of other elements including carbon, with the carbon not in excess of .2%.

9. An alloy consisting of chromium, nickel, copper and zinc in the approximate proportions of 41% nickel, 5% chromium, 42.5% copper, 10.8% 'zinc and traces of other elements includingcarbon withthe carbon content not.exceed-' ing 0.2%.

10. An alloycchsisting of chromium, nickel, copper and zinc in the approximate'proportions of 48.6 nickel, 7.2 chromium, 33.1 copper, and 10.4 zinc with traces of other elements including carbon, with the carbon content not exceeding 0.2%.

BIRGER EGEBERG. ROY w. mum. 

